1. Field of the Invention
The present invention relates to a method and apparatus for testing a magnetoresistive effect (MR) element used for a read head element of a thin-film magnetic head or for a magnetic memory.
2. Description of the Related Art
Recently, a lot of MR elements each having a multi-layered structure, such as giant magnetoresistive effect (GMR) elements or tunnel magnetoresistive effect (TMR) elements, are utilized as read head elements of thin-film magnetic heads in high recording density disk drive apparatus or as magnetic memories.
In general, each MR element with the multi-layered structure has a spacer layer or a tunnel barrier layer, a free layer and a pinned layer that sandwich the spacer layer or the tunnel barrier layer, a pinning layer for fixing a magnetization direction of the pinned layer, and domain control layers located at both side ends of the free layer in the track-width direction, for producing bias magnetic field that controls magnetic domain of the free layer.
In such multi-layered MR element, it was quite difficult to actually measure a uniaxial anisotropic magnetic field Hk of the free layer. This is because, to a free layer of a fabricated MR element, a bias magnetic field is always applied from magnetic domain control layers and thus the uniaxial anisotropic magnetic field Hk of the free layer will be disappeared from measurement by the bias magnetic field.
Because of this reason, any screening process in which a uniaxial anisotropic magnetic field Hk of the free layer is measured and whether the fabricated MR element is good product or not is judged depending upon the measured uniaxial anisotropic magnetic field Hk has been hardly performed.